Organic light-emitting display apparatus and method of manufacturing the same

ABSTRACT

An organic light-emitting display apparatus and a manufacturing method thereof have improved process stability and reliability by reducing damage to the organic light-emitting display apparatus during a manufacturing process. The organic light-emitting display apparatus includes: a substrate, a plurality of pixel electrodes, a pixel defining film, a plurality of hole control layers respectively arranged on the pixel electrodes, a plurality of emission layers respectively arranged on the hole control layers, a plurality of buffer layers respectively arranged on the emission layers, each of the buffer layers having a highest occupied molecular orbital (HOMO) energy level greater than the HOMO energy level of each of the plurality of emission layers, and an opposite electrode integrally provided over the buffer layers.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2018-0047314, filed on Apr. 24, 2018, in the KoreanIntellectual Property Office, the entire content of which isincorporated by reference.

BACKGROUND 1. Field

One or more embodiments of the present disclosure relate to an organiclight-emitting display apparatus and a method of manufacturing theorganic light-emitting display apparatus, and for example, to an organiclight-emitting display apparatus having improved process stability andreliability by reducing damage to an organic light-emitting device in amanufacturing process, and a method of manufacturing the organiclight-emitting display apparatus.

2. Description of the Related Art

Organic light-emitting display apparatuses are display apparatuses inwhich a pixel includes an organic light-emitting device. An organiclight-emitting device may include a pixel electrode, an oppositeelectrode facing the pixel electrode, and an emission layer providedbetween the pixel electrode and the opposite electrode.

For an organic light-emitting display apparatus implementing full color,respective pixel areas may emit light having colors that are differentfrom one another, and an emission layer of each pixel and an oppositeelectrode integrally formed in a plurality of pixels may be formed usinga deposition mask. As the resolution of an organic light-emittingdisplay apparatus gradually increases, the width of an open slit of amask used during a deposition process gradually decreases, and alsodispersion thereof is demanded to be gradually reduced. Furthermore, tomanufacture a high-resolution organic light-emitting display apparatus,a shadow effect should be reduced or eliminated. Accordingly, a methodof performing a deposition process when a substrate and a mask are inclose contact with each other may be used.

However, when a deposition process is performed when a substrate and amask are in close contact with each other, the mask may damage an upperlayer of a pixel electrode.

SUMMARY

One or more embodiments include an organic light-emitting displayapparatus having improved process stability and reliability by reducingdamage to an organic light-emitting device in a manufacturing process,and a manufacturing method thereof

Additional aspects of embodiments will be set forth in part in thedescription which follows and, in part, will be apparent from thedescription, or may be learned by practice of the presented embodiments.

According to one or more embodiments, a display apparatus includes asubstrate; a plurality of pixel electrodes patterned on the substrate tobe arranged spaced apart from each other; a pixel defining film defininga pixel area by exposing a center portion of each of the plurality ofpixel electrodes and covering an edge of each of the plurality of pixelelectrodes; a plurality of hole control layers respectively arranged onthe plurality of pixel electrodes that are exposed through the pixelarea; a plurality of emission layers respectively arranged on theplurality of hole control layers; a plurality of buffer layersrespectively arranged on the plurality of emission layers, each of theplurality of buffer layers having a highest occupied molecular orbital(HOMO) energy level greater than the HOMO energy level of each of theplurality of emission layers; and an opposite electrode integrallyprovided over the plurality of buffer layers.

A lowest unoccupied molecular orbital (LUMO) energy level of each of theplurality of buffer layers may have a value between a work function ofthe opposite electrode and the LUMO energy level of each of theplurality of emission layers.

Each of the plurality of hole control layers may include at least oneselected from a hole injection layer (HIL) and a hole transport layer(HTL).

The display apparatus may further include an electronic control layerthat is integrally provided between the plurality of buffer layers andthe opposite electrode.

The lowest unoccupied molecular orbital (LUMO) energy level of each ofthe plurality of buffer layers may have a value between the LUMO energylevel of the electronic control layer and the LUMO energy level of theplurality of emission layers.

The electronic control layer may include at least one selected from anelectron injection layer (EIL) and an electron transport layer (EML).

The plurality of buffer layers may include a low molecular weightorganic material.

The plurality of buffer layers may include an electron transportmaterial.

The plurality of buffer layers may include a metal oxide material.

The plurality of buffer layers may be arranged directly on the pluralityof emission layers to contact the plurality of emission layers.

End portions of the plurality of hole control layers, the plurality ofemission layers, and the plurality of buffer layers, which are on anyone of the plurality of pixel electrodes, may be aligned with oneanother.

The plurality of pixel electrodes may include a first pixel electrodefor red emission (e.g., configured to emit red light), a second pixelelectrode for green emission (e.g., configured to emit green light), anda third pixel electrode for blue emission (e.g., configured to emit bluelight), and the plurality of emission layers include a red emissionlayer (e.g., a layer configured to emit red light) providedcorresponding to the first pixel electrode, a green emission layer(e.g., a layer configured to emit green light) provided corresponding tothe second pixel electrode, and a blue emission layer (e.g., a layerconfigured to emit blue light) provided corresponding to the third pixelelectrode.

According to one or more embodiments, a method of manufacturing adisplay apparatus includes: (a) forming a first pixel electrode forfirst color emission, a second pixel electrode for second coloremission, and a third pixel electrode for third color emission, whereinthe first pixel electrode for first color emission, the second pixelelectrode for second color emission, and the third pixel electrode forthird color emission are patterned on a substrate to be spaced apartfrom one another; (b) forming a first lift-off layer including afluoropolymer on the first to third pixel electrodes; (c) forming afirst photoresist on the first lift-off layer; (d) sequentially forminga first opening and a second opening in the first photoresist and thefirst lift-off layer to expose the first pixel electrode, wherein thefirst photoresist and the first lift-off layer are formed at positionscorresponding to the first pixel electrode; (e) sequentially forming afirst hole control layer, a first emission layer, and a first bufferlayer, on the first pixel electrode, through the first opening and thesecond opening; (f) removing the first lift-off layer and the firstphotoresist; sequentially repeating operations (b) to (f) with respectto the second pixel electrode; and sequentially repeating operations (b)to (f) with respect to the third pixel electrode.

The sequentially repeating of operations (b) to (f) with respect to thesecond pixel electrode may include: (b) forming a second lift-off layeron the second to third pixel electrodes, the second lift-off layerincluding a fluoropolymer; (c) forming a second photoresist on thesecond lift-off layer; (d) sequentially forming a first opening and asecond opening in the second photoresist and the second lift-off layerto expose the second pixel electrode, wherein the second photoresist andthe second lift-off layer are formed at positions corresponding to thesecond pixel electrode; (e) sequentially forming a second hole controllayer, a second emission layer, and a second buffer layer, on the secondpixel electrode, through the first opening and the second opening; and(f) removing the second lift-off layer and the second photoresist,wherein the second buffer layer protects the second emission layer inthe removing of the second lift-off layer and the second photoresist.

The sequentially repeating of operations (b) to (f) with respect to thethird pixel electrode may include: (b) forming a third lift-off layer onthe third pixel electrodes, the third lift-off layer including afluoropolymer; (c) forming a third photoresist on the third lift-offlayer; (d) sequentially forming a first opening and a second opening inthe third photoresist and the third lift-off layer to expose the thirdpixel electrode, wherein the third photoresist and the third lift-offlayer are formed at positions corresponding to the third pixelelectrode; (e) sequentially forming a third hole control layer, a thirdemission layer, and a third buffer layer, on the third pixel electrode,through the first opening and the second opening; and (f) removing thethird lift-off layer and the third photoresist, wherein the third bufferlayer protects the third emission layer in the removing of the thirdlift-off layer and the third photoresist.

The method may further include forming an opposite electrode that isintegrally provided over the first buffer layer, the second bufferlayer, and the third buffer layer, wherein a lowest unoccupied molecularorbital (LUMO) energy level of the first buffer layer has a valuebetween a work function of the opposite electrode and the LUMO energylevel of the first emission layer.

The method may further include forming an electronic control layer thatis integrally provided over the first buffer layer, the second bufferlayer, and the third buffer layer; and forming an opposite electrodethat is integrally provided on the electronic control layer, wherein alowest unoccupied molecular orbital (LUMO) energy level of each of thefirst to third buffer layers has a value between the LUMO energy levelof the electronic control layer and the LUMO energy level of each of thefirst to third emission layers.

A highest occupied molecular orbital (HOMO) energy level of the firstbuffer layer may be greater than the HOMO energy level of the firstemission layer.

The first buffer layer may include at least one selected from a lowmolecular weight organic material, an electron transport material, and ametal oxide material.

End portions of the first hole control layer, the first emission layer,and the first buffer layer, which are above the first pixel electrode,may be aligned with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of embodiments will become apparent and morereadily appreciated from the following description of the embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view schematically illustrating a stackstructure of an organic light-emitting device according to anembodiment;

FIG. 2 is a cross-sectional view schematically illustrating a stackstructure of pixels according to an embodiment;

FIG. 3 is an energy bandgap diagram of an organic light-emitting deviceaccording to an embodiment;

FIG. 4 is a cross-sectional view schematically illustrating a stackstructure of an organic light-emitting device according to anotherembodiment;

FIG. 5 is a cross-sectional view schematically illustrating a stackstructure of an organic light-emitting device according to anotherembodiment;

FIG. 6 is a cross-sectional view schematically illustrating amanufacturing process of an organic light-emitting display apparatusaccording to another embodiment;

FIG. 7 is a cross-sectional view schematically illustrating amanufacturing process of an organic light-emitting display apparatusaccording to another embodiment;

FIGS. 8A-8H are cross-sectional views schematically illustrating amanufacturing process of an organic light-emitting display apparatusaccording to another embodiment;

FIGS. 9A-9E are cross-sectional views schematically illustrating amanufacturing process of an organic light-emitting display apparatusaccording to another embodiment;

FIGS. 10A-10E are cross-sectional views schematically illustrating amanufacturing process of an organic light-emitting display apparatusaccording to another embodiment; and

FIG. 11 is a cross-sectional view schematically illustrating amanufacturing process of an organic light-emitting display apparatusaccording to another embodiment.

DETAILED DESCRIPTION

As the present disclosure allows for various changes and numerousembodiments, embodiments of the present disclosure will be illustratedin the drawings and described in more detail in the written description.However, this is not intended to limit the present disclosure toparticular modes of practice, and it is to be appreciated that allchanges, equivalents, and substitutes that do not depart from the spiritand technical scope of the present disclosure are encompassed by thepresent disclosure. In the present disclosure, certain detailedexplanations of the related art are not provided when they would renderthe disclosure unclear.

The subject matter of the present disclosure will now be described inmore detail with reference to the accompanying drawings, in whichembodiments of the disclosure are shown. Throughout the drawings, likereference numerals denote like elements. In the following description,when detailed descriptions about related well-known functions orstructures would render the present disclosure unclear, those detaileddescriptions will not be provided.

It will be understood that although the terms “first,” “second,” etc.may be used herein to describe various components, these componentsshould not be limited by these terms. These components are only used todistinguish one component from another. As used herein, the singularforms “a,” “an,” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise.

It will be further understood that the terms “comprises” and/or“comprising” used herein specify the presence of stated features orcomponents, but do not preclude the presence or addition of one or moreother features or components. Furthermore, it will be understood thatwhen a layer, region, or component is referred to as being “formed on”another layer, region, or component, it can be directly or indirectlyformed on the other layer, region, or component. For example,intervening layers, regions, or components may be present.

Sizes of components in the drawings may be exaggerated for convenienceof explanation. In other words, since sizes and thicknesses ofcomponents in the drawings may be arbitrarily illustrated forconvenience of explanation, the following embodiments are not limitedthereto.

In the following examples, the x-axis, the y-axis and the z-axis are notlimited to three axes of the rectangular coordinate system, and may beinterpreted in a broader sense. For example, the x-axis, the y-axis, andthe z-axis may be perpendicular (e.g., substantially perpendicular) toone another, or may represent different directions that are notperpendicular to one another.

When a certain embodiment may be implemented differently, a specificprocess order may be performed differently from the described order. Forexample, two consecutively described processes may be performedconcurrently (e.g., substantially at the same time) or performed in anorder opposite to the described order.

FIG. 1 is a cross-sectional view schematically illustrating a stackstructure of an organic light-emitting device 1 according to anembodiment.

Referring to FIG. 1, an organic light-emitting display apparatusaccording to an embodiment may include the organic light-emitting device1. The organic light-emitting device 1 may include a pixel electrode 10,an opposite electrode 30 above the pixel electrode 10, and anintermediate layer 20 between the pixel electrode 10 and the oppositeelectrode 30. The intermediate layer 20 may include a hole control layer20H, an emission layer 23 on the hole control layer 20H, a buffer layer24 on the emission layer 23, and an electronic control layer 20E on thebuffer layer 24. In this case, the hole control layer 20H may optionallyinclude a hole injection layer 21 (see FIG. 4) and a hole transportlayer 22 (see FIG. 4), and the electronic control layer 20E mayoptionally include an electron injection layer 26 (see FIG. 4) and anelectron transport layer 25 (see FIG. 4).

In the present embodiment, the buffer layer 24 may be on the emissionlayer 23. The electronic control layer 20E, which optionally includesthe electron injection layer 26 and the electron transport layer 25, maybe on the buffer layer 24, or the opposite electrode 30 may be directlyon the buffer layer 24 without the electronic control layer 20Etherebetween.

The buffer layer 24 may include an organic material and/or a metal oxidematerial. When the buffer layer 24 includes an organic material, thebuffer layer 24 may include, for example, a low molecular weight organicmaterial including at least one selected from BAlq(bis(2-methyl-8-quinolinolate)-4-(phenylphenolato)aluminium), BCP(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), DTBT(Dithienylbenzothiadiazole), TPBi(1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene), PBD(2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4oxadiazole), TAZ(3-(4-biphenyl)4-phenyl-5-tert-butylphenyl-1,2,4-triazole), C60F42, Liq(8-hydroxyquinolinolato-lithium), and spiro-PBD, and/or at least oneselected from an oligomer, polymer, and a copolymer derivative based onthe low molecular weight organic material.

Furthermore, when the buffer layer 24 includes an organic material, thebuffer layer 24 may include, for example, BND, OXD-7, OXD-star,Alq3(tris-(8-hydroyquinolato) aluminum(III)), Bphen, NTAZ, Bphen(4,7-diphenyl-1,10-phenanthroline), NTAZ(4-(naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazole), t-Bu-PBD(2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole), t-Bu-PND,Bebq2 (Bis(10-hydroxybenzo[h]quinolinato)beryllium), ADN(9,10-bis(2-naphthyl)anthracene), or a mixture thereof.

Furthermore, when the buffer layer 24 includes a metal oxide material,the buffer layer 24 may include, for example, CuOx, MoOx, WOx, ZnO, or amixture thereof. In this case, a doping material may be added to thebuffer layer 24 to improve electrical properties of the buffer layer 24and to secure process stability.

Furthermore, when the buffer layer 24 includes an organic material, theorganic material may have a structure in which, for example, at leastsome of the molecules are cross-linked with each other by way of achemical a bond such as a C—O, C—C, C—N, C—S, C═C, and/or C═O bond, tohave a bonding energy of 60 kcal/mol or more.

In the present embodiment, the buffer layer 24 that is directly on theemission layer 23 may protect the emission layer 23 from being damagedand oxidized in a subsequent process. This is described herein below inmore detail in the description of a manufacturing method shown in FIG. 6and the description and drawings following thereafter.

FIG. 2 is a cross-sectional view schematically illustrating a stackstructure of pixels R, G, and B according to an embodiment.

Referring to FIG. 2, an organic light-emitting display apparatusaccording to an embodiment may include a plurality of pixel electrodes10R, 10G, and 10B. Although FIG. 2 illustrates that, for convenience ofexplanation, the pixel electrodes 10R, 10G, and 10B are in contact withone another, the pixel electrodes 10R, 10G, and 10B may be patterned tobe spaced apart from one another.

The pixel electrodes 10R, 10G, and 10B may include a first pixelelectrode 10R for red (R) emission (e.g., the first pixel electrode 10Remits light having a red color), a second pixel electrode 10G for green(G) emission (e.g., the second pixel electrode 10G emits light having agreen color), and a third pixel electrode 10B for blue (B) emission(e.g., the first pixel electrode 10B emits light having a blue color).First, second, and third hole injection layers 21R, 21G, and 21B andfirst, second, and third hole transport layers 22R, 22G, and 22B may berespectively on and above the first, second, and third pixel electrodes10R, 10G, and 10B. The first, second, and third hole injection layers21R, 21G, and 21B and the first, second, and third hole transport layers22R, 22G, and 22B may correspond to the hole control layer 20H describedin FIG. 1. In the present embodiment, although the hole control layer20H includes all of the first, second, and third hole injection layers21R, 21G, and 21B and the first, second, and third hole transport layers22R, 22G, and 22B, the hole control layer 20H may, optionally,selectively include the first, second, and third hole injection layers21R, 21G, and 21B and the first, second, and third hole transport layers22R, 22G, and 22B, as is desired or necessary. For example, the holecontrol layer 20H may include only the first, second, and third holeinjection layers 21R, 21G, and 21B, or the hole control layer 20H mayinclude only the first, second, and third hole transport layers 22R,22G, and 22B. In some embodiments, the hole control layer 20H mayinclude only one of the first, second, and third hole injection layers21R, 21G, and 21B, or the hole control layer 20H may include only one ofthe first, second, and third hole transport layers 22R, 22G, and 22B.

The first, second, and third hole injection layers 21R, 21G, and 21B mayinclude, for example, a phthalocyanine compound such as copperphthalocyanine; DNTPD(N,N′-diphenyl-N,N′-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4′-diamine),m-MTDATA(4,4′,4″-tris(3-methylphenylphenylamino) triphenylamine),TDATA(4,4′4″-Tris(N,N-diphenylamino)triphenylamine),2TNATA(4,4′,4″-tris{N,-(2-naphthyl)-N-phenylamino}-triphenylamine),PEDOT/PSS(Poly(3,4-ethylenedioxythiophene)/Poly(4-styrenesulfonate),PANI/DBSA(Polyaniline/Dodecylbenzenesulfonic acid),PANI/CSA(Polyaniline/Camphor sulfonic acid), and/orPANI/PSS((Polyaniline)/Poly(4-styrenesulfonate, but a material includedthe hole injection layers is not limited to the above-describedcompounds.

The first, second, and third hole transport layers 22R, 22G, and 22B mayinclude, for example, N-phenylcarbazole, a carbazole-based derivativesuch as polyvinylcarbazole, a fluorine-based derivative,TPD(N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1-biphenyl]-4,4′-diamine),a triphenylamine-based derivative such asTCTA(4,4′,4″-tris(N-carbazolyl)triphenylamine),NPB(N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine), and/orTAPC(4,4′-Cyclohexylidene bis[N,N-bis(4-methylphenyl)benzenamine]), butthe present disclosure is not limited thereto.

First, second, and third emission layers 23R, 23G, and 23B may berespectively on the first, second, and third hole transport layers 22R,22G, and 22B. In other words, the red (R) emission layer 23R may be onthe first pixel electrode 10R, the green (G) emission layer 23G may beon the second pixel electrode 10G, and the blue (B) emission layer 23Bmay be on the third pixel electrode 10B.

As an optional embodiment, a first auxiliary layer SL_R corresponding toa resonance control layer may be between the first hole transport layer22R and the first emission layer 23R. Furthermore, a second auxiliarylayer SL_G corresponding to a resonance control layer may be between thesecond hole transport layer 22G and the second emission layer 23G. Asnecessary or desired, an auxiliary layer may be provided between thethird hole transport layer 22B and the third emission layer 23B.

First, second, and third buffer layers 24R, 24G, and 24B may berespectively on the first, second, and third emission layers 23R, 23G,and 23B. In other words, the first buffer layer 24R may be on the red(R) emission layer 23R, the second buffer layer 24G may be on the green(G) emission layer 23G, and the third buffer layer 24B may be on theblue (B) emission layer 23B. The first, second, and third buffer layers24R, 24G, and 24B may correspond to the buffer layer 24 described inFIG. 1.

The electron transport layer 25 may be on the first, second, and thirdbuffer layers 24R, 24G, and 24B. The electron transport layer 25, whichis a common layer, may be integrally provided on the first, second, andthird buffer layers 24R, 24G, and 24B. The electron transport layer 25may include, for example, Alq3(Tris(8-hydroxyquinolinato)aluminum),TPBi(1,3,5-Tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl),BCP(2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline),Bphen(4,7-Diphenyl-1,10-phenanthroline),TAZ(3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole),NTAZ(4-(Naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazole),tBu-PBD(2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole),BAlq(Bis(2-methyl-8-quinolinolato-N1,O8)-(1,1′-Biphenyl-4-olato)aluminum),Bebq2(berylliumbis(benzoquinolin-10-olate),ADN(9,10-di(naphthalene-2-yl)anthracene), or a mixture thereof, but thepresent disclosure is not limited thereto.

In some embodiments, the electron injection layer 26 may be furtherprovided between the opposite electrode 30 and the electron transportlayer 25, as shown in FIG. 4. The electron injection layer 26 mayinclude, for example, a lanthanum series metal (or a compound includinga lanthanum series metal) such as LiF, LiQ (Lithium quinolate), Li₂O,BaO, NaCl, CsF, or Yb, or a halogenated metal such as RbCl or Rbl, butthe present disclosure is not limited thereto.

Referring back to FIG. 2, the opposite electrode 30 may be over thefirst, second, and third buffer layers 24R, 24G, and 24B. The oppositeelectrode 30, which is a common layer, may be integrally provided on theelectron transport layer 25.

Optionally, a capping layer 40 and an encapsulation layer 50 may befurther provided on the opposite electrode 30.

As illustrated in FIG. 2, the electron transport layer 25, the oppositeelectrode 30, the capping layer 40, and the encapsulation layer 50,which are on the first, second, and third buffer layers 24R, 24G, and24B, may be provided as common layers. In contrast, layers under thefirst, second, and third buffer layers 24R, 24G, and 24B may be providedby being patterned for each pixel. In other words, the first, second,and third pixel electrodes 10R, 10G, and 10B may be patterned for eachpixel, a pixel defining film may be provided to cover edges of thefirst, second, and third pixel electrodes 10R, 10G, and 10B, the first,second, and third hole injection layers 21R, 21G, and 21B, the first,second, and third hole transport layers 22R, 22G, and 22B, the first,second, and third emission layers 23R, 23G, and 23B, and the first,second, and third buffer layers 24R, 24G, and 24B may be patterned andprovided on the first, second, and third pixel electrodes 10R, 10G, and10B which are exposed through an opening of the pixel defining film.This is described herein below in more detail in the description of themanufacturing method illustrated in FIG. 6 and the description anddrawings following thereafter.

FIG. 3 is an energy bandgap diagram of an organic light-emitting deviceaccording to an embodiment.

In FIG. 3, an organic light-emitting device including the hole injectionlayer 21, the hole transport layer 22, the emission layer 23, the bufferlayer 24, and the electron transport layer 25 between the pixelelectrode 10 and the opposite electrode 30 is illustrated.

Referring to FIG. 3, according to an embodiment, a highest occupiedmolecular orbital (HOMO) energy level 24H of the buffer layer 24 may becharacteristically greater than a HOMO energy level 23_H of the emissionlayer 23. In an embodiment in which the electron transport layer 25 ison the buffer layer 24, a lowest unoccupied molecular orbital (LUMO)energy level 24_L of the buffer layer 24 may have a value between a LUMOenergy level 25_L of the electron transport layer 25 and a LUMO energylevel 23_L of the emission layer 23.

In another embodiment, an organic light-emitting display apparatusaccording to an embodiment may include an organic light-emitting deviceincluding the hole injection layer 21, the hole transport layer 22, theemission layer 23, and the buffer layer 24 between the pixel electrode10 and the opposite electrode 30.

In this case, the HOMO energy level 24_H of the buffer layer 24 may becharacteristically greater than the HOMO energy level 23_H of theemission layer 23. Furthermore, the LUMO energy level 24_L of the bufferlayer 24 may have a value between a work function of the oppositeelectrode 30 and the LUMO energy level 23_L of the emission layer 23.

The buffer layer 24 according to an embodiment is directly on theemission layer 23 to protect the emission layer 23 from being damagedand oxidized in a subsequent process. However, there is an issue ofefficiency of an organic light-emitting device being degraded due to thebuffer layer 24 provided in the intermediate layer 20, which needs to beaddressed. Accordingly, the characteristics of the buffer layer 24 areto prevent the holes injected from the pixel electrode 10 into theemission layer 23 from being transmitted to the electron transport layer25 or the opposite electrode 30 (or to reduce the transmission of theholes to the electron transport layer 25 or the opposite electrode 30),and thus the buffer layer 24 may prevent or reduce the degradation ofthe characteristics of an organic light-emitting device.

FIG. 4 is a cross-sectional view schematically illustrating a stackstructure of an organic light-emitting device 2 according to anotherembodiment. FIG. 5 is a cross-sectional view schematically illustratinga stack structure of an organic light-emitting device 3 according toanother embodiment.

Referring to FIG. 4, an organic light-emitting display apparatusaccording to another embodiment may include the organic light-emittingdevice 2. The organic light-emitting device 2 of FIG. 4 is substantiallythe same as the organic light-emitting device 1 of FIG. 1, except thatthe hole control layer 20H includes the hole injection layer 21 and thehole transport layer 22, and that the electronic control layer 20Eincludes the electron injection layer 26 and the electron transportlayer 25.

The organic light-emitting device 2 may include the pixel electrode 10,the opposite electrode 30 above the pixel electrode 10, and theintermediate layer 20 between the pixel electrode 10 and the oppositeelectrode 30. The intermediate layer 20 may include the hole injectionlayer 21, the hole transport layer 22 on the hole injection layer 21,the emission layer 23 on the hole transport layer 22, the buffer layer24 on the emission layer 23, the electron transport layer 25 on thebuffer layer 24, and the electron injection layer 26 on the electrontransport layer 25.

Referring to FIG. 5, an organic light-emitting display apparatusaccording to another embodiment may include the organic light-emittingdevice 3. The organic light-emitting device 3 illustrated in FIG. 5 issubstantially the same as the embodiment of FIG. 1, except that the holecontrol layer 20H includes the hole injection layer 21 and the holetransport layer 22, that the electronic control layer 20E includes theelectron injection layer 26, and that the organic light-emitting device3 a includes a first buffer layer 24 a and a second buffer layer 24 b.

The organic light-emitting device 3 may include the pixel electrode 10,the opposite electrode 30 above the pixel electrode 10, and theintermediate layer 20 between the pixel electrode 10 and the oppositeelectrode 30. The intermediate layer 20 may include the hole injectionlayer 21, the hole transport layer 22 on the hole injection layer 21,the emission layer 23 on the hole transport layer 22, the first bufferlayer 24 a on the emission layer 23, the second buffer layer 24 b on thefirst buffer layer 24 a, and the electron injection layer 26 on thesecond buffer layer 24 b.

The above-described embodiments of FIGS. 4-5 are example embodiments,and the present disclosure is not limited to the thicknesses of thelayers illustrated in the drawings. The thickness and number of thebuffer layer 24 may vary according to the configuration of theintermediate layer 20.

Although an organic light-emitting display apparatus is mainly describedin the above description, the present disclosure is not limited thereto.For example, a method of manufacturing the above-described organiclight-emitting display apparatus is also within the scope of the presentdisclosure.

FIGS. 6-10E are cross-sectional views schematically illustrating amanufacturing process of an organic light-emitting display apparatusaccording to an embodiment.

First, referring to FIG. 6, a first pixel electrode 101 for first coloremission (e.g., a first pixel electrode configured to emit a first colorof light), a second pixel electrode 102 for second color emission (e.g.,a second pixel electrode configured to emit a second color of light),and a third pixel electrode 103 for third color emission (e.g., a thirdpixel electrode configured to emit a third color of light) may be formedon a substrate 100. The first pixel electrode 101, the second pixelelectrode 102, and the third pixel electrode 103 may be patterned to bearranged spaced apart from one another.

The arrangement of the first, second, and third pixel electrodes 101,102, and 103 on the substrate 100 may include not only a case in whichthe first, second, and third pixel electrodes 101, 102, and 103 aredirectly arranged on the substrate 100, but also a case in which varioussuitable layers are formed on the substrate 100 and the first, second,and third pixel electrodes 101, 102, and 103 are arranged on the varioussuitable layers. For example, a thin film transistor may be on thesubstrate 100, a planarization film may cover the thin film transistor,and the first, second, and third pixel electrodes 101, 102, and 103 maybe on the planarization film. Although the drawings illustrate that, forconvenience of explanation, the first, second, and third pixelelectrodes 101, 102, and 103 are directly on the substrate 100, theabove description may also apply to the following description, forconvenience of explanation.

The substrate 100 may be formed of various suitable materials. Forexample, the substrate 100 may be formed of glass and/or plastic. Thesubstrate 100 may be formed of a material having excellent heatresistance and durability such as polyimide, polyethylenenaphthalate,polyethyleneterephthalate, polyarylate, polycarbonate, polyetherimide,and/or polyethersulfone.

The first, second, and third pixel electrodes 101, 102, and 103 formedon the substrate 100 may be formed as (semi-)transparent electrodes orreflective electrodes. When the first, second, and third pixelelectrodes 101, 102, and 103 are formed as (semi)transparent electrodes,the first, second, and third pixel electrodes 101, 102, and 103 may beformed of, for example, ITO, IZO, ZnO, In₂O₃, IGO, and/or AZO. When thefirst, second, and third pixel electrodes 101, 102, and 103 are formedas reflective electrodes, each of the first, second, and third pixelelectrodes 101, 102, and 103 may have a reflective film formed of Ag,Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, and/or a compound thereof and alayer formed of ITO, IZO, ZnO, In₂O₃, IGO, and/or AZO. The presentdisclosure is not limited thereto, and a variety of suitablemodifications may be made. For example, the first, second, and thirdpixel electrodes 101, 102, and 103 may be formed of various suitablematerials in a single layer or a multilayer.

Next, as illustrated in FIG. 7, a pixel defining film 110 that exposes acenter portion of each of the first pixel electrode 101, the secondpixel electrode 102, and the third pixel electrode 103 and covers anedge portion thereof may be formed. The pixel defining film 110 definesa pixel area and prevents or reduces generation of arcs during drivingas an electric field concentrates on end portions of the first, second,and third pixel electrodes 101, 102, and 103.

The pixel defining film 110 may be provided as, for example, an organicinsulating film. An organic insulating film may include an acrylic-basedpolymer such as polymethyl methacrylate (PMMA), polystyrene (PS), apolymer derivative having a phenol group, an imide-based polymer, anaryl ether-based polymer, an amide-based polymer, a fluorine-basedpolymer, a p-xylene-based polymer, a vinyl alcohol-based polymer, or amixture thereof.

Next, as illustrated in FIGS. 8A-8H, an intermediate layer 101A (seeFIG. 8H) may be formed on the first pixel electrode 101. Theintermediate layer 101A may mean a first hole injection layer 141, afirst hole transport layer 151, a first emission layer 161, and a firstbuffer layer 171. An electronic control layer such as an electrontransport layer may be further formed in a subsequent process.

The processes of FIGS. 8A-8H may be construed as a first unit processcorresponding to the first pixel electrode 101. Then, a second unitprocess corresponding to the second pixel electrode 102 may be performedthrough processes of FIGS. 9A-9E, and a third unit process correspondingto the third pixel electrode 103 may be performed through processes ofFIGS. 10A-10E. In this case, the first unit process, the second unitprocess, and the third unit process may be the same process that isrepeatedly performed.

First, referring to FIG. 8A, a first lift-off layer 121 including afluoropolymer may be formed on the first pixel electrode 101, the secondpixel electrode 102, and the third pixel electrode 103. Thefluoropolymer included in the first lift-off layer 121 may be formed asa polymer including a fluorine content of 20 to 60 wt %. For example,the fluoropolymer may include at least one copolymer selected from acopolymer of polytetrafluoroethylene, polychlorotrifluoroethylene,polydichlorodifluoroethylene, chlorotrifluoroethylene, anddichlorodifluoroethylene; a copolymer of tetrafluoroethylene andperfluoroalkylvinylether; a copolymer of chlorotrifluoroethylene andperfluoro alkyl vinyl ether; a copolymer tetrafluoroethylene; and acopolymer of chlorotrifluoroethylene and perfluoroalkylvinylether.

The first lift-off layer 121 may be formed on the substrate 100 by amethod such as a coating method, a printing method, or a depositionmethod. When the first lift-off layer 121 is formed by a coating methodand a printing method, a process of forming photoresist may be performedafter performing curing and polymerization as necessary.

The thickness of the first lift-off layer 121 may be between 0.2 μm and5.0 μm. When the thickness of the first lift-off layer 121 is too large,a time to melt the first lift-off layer 121 for patterning may increase,and thus a manufacturing processing time may be extended. When thethickness of the first lift-off layer 121 is too small, it is difficultto perform lift off.

The first lift-off layer 121 may further include a moisture absorbent.The moisture absorbent may include various suitable materials. Themoisture absorbent may be a compound in which metals such as calcium(e.g., calcium oxide), barium (e.g., barium oxide), aluminum (e.g.,aluminum oxide), and/or magnesium (e.g., magnesium oxide) are coupled(or connected) by oxygen, and may include a material that forms metalhydroxide when reacting with water. Furthermore, the moisture absorbentmay include any one selected from a group consisting of a metal halide,an inorganic salt of metal, an organic acid salt, a porous inorganiccompound, and a combination thereof. The moisture absorbent may includean acrylic-based, methacrylic-based, polyisoprene-based, vinyl-based,epoxy-based, urethane-based, and/or cellulosic-based organic material.The moisture absorbent may include a titania-, silicon oxide-,zirconia-, and/or alumina-based inorganic material. The moistureabsorbent may include a sealant manufactured from epoxy silane, vinylsilane, amine silane, and/or methacrylate silane. The moisture absorbentmay capture moisture generated during the first unit process and thusprevent or reduce degradation of the first emission layer 161 formedduring the first unit process.

A first photoresist 131 may be formed on the first lift-off layer 121.The first photoresist 131 may be exposed or developed by using a firstphotomask. The first photoresist 131 may be of either a positive type(or kind) or a negative type (or kind). In the present embodiment, anexample of a positive type (or kind) is described herein below.

Referring to FIG. 8B, the first photoresist 131 is patterned. The firstphotoresist 131 that is exposed and developed is removed from a firstportion 131-1 that is a position corresponding to the first pixelelectrode 101, and the first photoresist 131 remains in a second portion131-2 that is an area other than the first portion 131-1. A firstopening OP1 may be formed in the first photoresist 131 corresponding tothe first portion 131-1.

Referring to FIG. 8C, the first lift-off layer 121 is etched by using apattern of the first photoresist 131 of FIG. 8B as an etch mask.

Since the first lift-off layer 121 includes a fluoropolymer, a solventcapable of etching the fluoropolymer may be used as an etchant. A firstsolvent including fluorine may be used as an etchant. The first solventmay include a hydrofluoroether. Hydrofluoroethers are electrochemicallystable material due to low interaction reactivity with other materials,and are also an environmentally stable material due to a low globalwarming potential and low toxicity.

In an etching process, the first lift-off layer 121 formed at a positioncorresponding to the first portion 131-1, that is, on an upper side ofthe first pixel electrode 101, is etched. The first lift-off layer 121is etched to be spaced apart a set or certain distance from a sidesurface of the first pixel electrode 101 by forming a first undercutprofile UC1 under a boundary surface of the first portion 131-1 of thefirst photoresist 131. Accordingly, a second opening OP2 may be formedin the first lift-off layer 121 corresponding to the first portion131-1. The first pixel electrode 101 may be exposed through the secondopening OP2.

Referring to FIG. 8D, an intermediate layer may be formed on the firstphotoresist 131. The intermediate layer may include the first emissionlayer 161. Furthermore, the intermediate layer may further include atleast one selected from organic functional layers such as a holeinjection layer, a hole transport layer, an electron transport layer,and an electron injection layer.

In the present embodiment, a case in which the intermediate layerincludes a hole injection layer, a hole transport layer, and an electrontransport layer is described as an example, but the present disclosureis not limited thereto.

In the present embodiment, the intermediate layer may be formed by avacuum deposition method. In a deposition process, the first lift-offlayer 121 and the first photoresist 131 perform a deposition maskfunction. A part of the intermediate layer may cover an upper surface ofthe first pixel electrode 101. The other part of the intermediate layeris formed on the second portion 131-2 of the first photoresist 131.

Referring to FIG. 8D, the first hole injection layer 141 is formed onthe structure of FIG. 8C. A part of the first hole injection layer 141may be formed on the first pixel electrode 101 through the first openingOP1 and the second opening OP2 formed in the first photoresist 131 andthe first lift-off layer 121, which serve as a mask. The other part ofthe first hole injection layer 141 may be formed on the second portion131-2 of the first photoresist 131.

Next, referring to FIG. 8E, the first hole transport layer 151 is formedon the structure of FIG. 8D. A part of the first hole transport layer151 may be formed on the first hole injection layer 141 corresponding tothe first pixel electrode 101 through the first opening OP1 and thesecond opening OP2. Other part of the first hole transport layer 151 maybe formed on the second portion 131-2 on which the first hole injectionlayer 141 is formed.

Next, referring to FIG. 8F, the first emission layer 161 is formed onthe structure of FIG. 8E. A part of the first emission layer 161 may beformed on the first hole transport layer 151 corresponding to the firstpixel electrode 101 through the first opening OP1 and the second openingOP2. Other part of the first emission layer 161 may be formed on thesecond portion 131-2 on which the first hole transport layer 151 isformed. In the present embodiment, the first emission layer 161 may be ared emission layer (e.g., a layer configured to emit red light), but thepresent disclosure is not limited thereto.

Next, referring to FIG. 8G, the first buffer layer 171 may be formed onthe structure of FIG. 8F. A part of the first buffer layer 171 may beformed on the first emission layer 161 corresponding to the first pixelelectrode 101 through the first opening OP1 and the second opening OP2.Another part of the first buffer layer 171 may be formed on the secondportion 131-2 on which the first emission layer 161 is formed.

Since the first buffer layer 171 is formed directly on the firstemission layer 161, the first buffer layer 171 may perform a barrierfunction to protect the first emission layer 161 from the solvent usedin subsequent processes after the formation of the first emission layer161. The first buffer layer 171 includes the same material (e.g.,substantially the same material) and has the same (e.g., substantiallythe same) characteristics as those of the buffer layer 24 described inFIGS. 1-3, and thus, a redundant description thereof is not repeatedhere.

Next, referring to FIG. 8H, a lift-off process is performed on thestructure of FIG. 8G.

By lifting off the first lift-off layer 121 formed under the secondportion 131-2 of the first photoresist 131, the first hole injectionlayer 141, the first hole transport layer 151, the first emission layer161, and the first buffer layer 171, which are formed in the secondportion 131-2 of the first photoresist 131, are removed, and thus, thefirst hole injection layer 141, the first hole transport layer 151, thefirst emission layer 161, and the first buffer layer 171, which areformed on the first pixel electrode 101, remain as a pattern.

Since the first lift-off layer 121 includes a fluoropolymer, a secondsolvent including fluorine is used in the lift-off process.Additionally, since the lift-off process is performed after theformation of the first emission layer 161, a material having lowreactivity with the first emission layer 161 may be used as the secondsolvent. For example, the second solvent may include a hydrofluoroether,like the first solvent.

However, in spite of using a material having low reactivity with thefirst emission layer 161 as the second solvent, there is a problem inthat the first emission layer 161 may be damaged during the lift-offprocess due to a component that decomposes (or dissolves) organicmaterials.

In a deposition process for forming an organic light-emitting device, alow molecular weight organic material (e.g., small molecules) havingadvantages in terms of synthetic reproducibility, characteristics, andprocessability is used as a material used as an organic material.However, in a thin film structure formed of a low molecular weightorganic material, the respective molecules interact through van derWaals bonding (e.g., van der Waals forces), hydrogen bonding, and/or π-πstacking bonding, which provide low non-covalent interaction energy ofabout 30 kcal/mol. Accordingly, the low molecular weight organicmaterial may be easily decomposed (or dissolved) in a solution processsuch as, for example, an orthogonal solvent process. The organicmaterial decomposed (or dissolved) as described above may damage theemission layer 23, thereby degrading the quality of a pixel.

Accordingly, according to an embodiment, since the first buffer layer171 is formed directly on the first emission layer 161 so that the firstbuffer layer 171 covers the first emission layer 161, damage to thefirst emission layer 161 by the solvent in the subsequent lift-offprocess may be reduced.

The first unit process of FIGS. 8A-8H may be repeatedly performed in thesecond unit process of FIGS. 9A-9E and the third unit process of FIGS.10A-10E, which are described in more detail herein below.

The second unit process corresponding to the second pixel electrode 102are described herein below with reference to FIGS. 9A-9E.

Referring to FIG. 9A, a second lift-off layer 122 including afluoropolymer and a second photoresist 132 may be sequentially formed onthe substrate 100 on which the structure of FIG. 8H is formed.

The second lift-off layer 122 may be formed by a method such as acoating method, a printing method, or a deposition method. The secondlift-off layer 122 may be formed of the same material (e.g.,substantially the same material) as the first lift-off layer 121 that isdescribed herein above.

The second photoresist 132 may be exposed and developed by using asecond photomask. The second photoresist 132 may be of either a positivetype (or kind) or a negative type (or kind). In the present embodiment,an example of a positive type (or kind) is described herein below.

Next, referring to FIG. 9B, the second photoresist 132 is patterned. Thesecond photoresist 132 that is exposed and developed is removed from afirst portion 132-1 that is a position corresponding to the second pixelelectrode 102, and the second photoresist 132 remains in a secondportion 132-2 that is an area other than the first portion 132-1.

Next, referring to FIG. 9C, the second lift-off layer 122 is etched byusing a pattern of the second photoresist 132 of FIG. 9B as an etchmask. Since the second lift-off layer 122 includes a fluoropolymer, asolvent capable of etching the fluoropolymer may be used as an etchant.A first solvent including fluorine may be used as an etchant. The firstsolvent may include a hydrofluoroether as in the above-described firstunit process. The first solvent may include a material different fromthat used in the first unit process.

The second lift-off layer 122 formed at a position corresponding to afirst portion 132-1, for example, on the second pixel electrode 102, isetched by an etching process. The second lift-off layer 122 is etched tobe spaced apart a set or certain distance from a side surface of thesecond pixel electrode 102 by forming a second undercut profile UC2under a boundary surface of the first portion 132-1 of the secondphotoresist 132.

Next, referring to FIG. 9D, as in FIGS. 8D-8G, a second hole injectionlayer 142, a second hole transport layer 152, a second emission layer162, and a second buffer layer 172 may be sequentially deposited on thesecond pixel electrode 102. In the present embodiment, the secondemission layer 162 may be a green emission layer (e.g., a layerconfigured to emit green light), but the present disclosure is notlimited thereto.

Next, referring to FIG. 9E, a lift-off process is performed on thestructure of FIG. 9D.

By lifting off the second lift-off layer 122 formed under a secondportion 132-2 of the second photoresist 132, the second hole injectionlayer 142, the second hole transport layer 152, the second emissionlayer 162, and the second buffer layer 172, which are formed in thesecond portion 132-2 of the second photoresist 132, are removed, and thesecond hole injection layer 142, the second hole transport layer 152,the second emission layer 162, and the second buffer layer 172, whichare formed on the second pixel electrode 102, remain as a pattern.

Since the second lift-off layer 122 includes a fluoropolymer, a secondsolvent including fluorine is used in the lift-off process.Additionally, since the lift-off process is performed after theformation of the second emission layer 162, a material having lowreactivity with the second emission layer 162 may be used as the secondsolvent. For example, the second solvent may include a hydrofluoroether,like the first solvent.

However, in spite of using a material having low reactivity with thesecond emission layer 162 as the second solvent, there is a problem inthat the second emission layer 162 may be damaged during the lift-offprocess due to a component that decomposes (or dissolves) organicmaterials.

Concurrently, there is a problem in that damage to the first emissionlayer 161 may be accumulated because the first emission layer 161 thatis first formed in the manufacture of the previous structure is exposedto the second solvent in the lift-off process included in the secondunit process, and exposed to the lift-off process several times as eachunit process is repeated for each pixel.

Accordingly, in the organic light-emitting display apparatus accordingto an embodiment, and a manufacturing method thereof, since the firstbuffer layer 171 is formed on the first emission layer 161, the secondbuffer layer 172 is formed on the second emission layer 162, and thefirst buffer layer 171 and the second buffer layer 172 serve asbarriers, damage to the first emission layer 161 and the second emissionlayer 162 during the lift-off process may be reduced.

The third unit process corresponding to the third pixel electrode 103 isdescribed with reference to FIGS. 10A-10E.

Referring to FIG. 10A, a third lift-off layer 123 including afluoropolymer and a third photoresist 133 may be sequentially formed onthe substrate 100 on which the structure of FIG. 9E is formed.

The third lift-off layer 123 may be formed by a method such as a coatingmethod, a printing method, or a deposition method. The third lift-offlayer 123 may be formed of the same material (e.g., substantially thesame material) as that of the first and second lift-off layers 121 and122.

The third photoresist 133 may be exposed and developed by using a thirdphotomask. The third photoresist 133 may be of either a positive type(or kind) or a negative type (or kind). In the present embodiment, anexample of a positive type (or kind) is described herein below.

Next, referring to FIG. 10B, the third photoresist 133 is patterned. Thethird photoresist 133 that is exposed and developed is removed from afirst portion 133-1 that is a position corresponding to the third pixelelectrode 103, and the third photoresist 133 remains in a second portion133-2 that is an area other than the first portion 133-1.

Next, referring to FIG. 10C, the third lift-off layer 123 is etched byusing a pattern of the third photoresist 133 of FIG. 10B as an etchmask. Since the third lift-off layer 123 includes a fluoropolymer, asolvent capable of etching the fluoropolymer may be used as an etchant.A first solvent including fluorine may be used as an etchant. The firstsolvent may include a hydrofluoroether as in the above-described firstunit process. The first solvent may include a material different fromthat used in the first unit process.

The third lift-off layer 123 formed at a position corresponding to afirst portion 133-1, for example, on the third pixel electrode 103, isetched by an etching process. The third lift-off layer 123 is etched tobe spaced apart a set or certain distance from a side surface of thethird pixel electrode 103 by forming a third undercut profile UC3 undera boundary surface of the first portion 133-1 of the third photoresist133.

Next, referring to FIG. 10D, as in FIGS. 8D-8G, a third hole injectionlayer 143, a third hole transport layer 153, a third emission layer 163,and a third buffer layer 173 may be sequentially deposited on the thirdpixel electrode 103. In the present embodiment, the third emission layer163 may be a blue emission layer (e.g., a layer configured to emit bluelight), but the present disclosure is not limited thereto.

Next, referring to FIG. 10E, a lift-off process is performed on thestructure of FIG. 10D.

By lifting off the third lift-off layer 123 formed under a secondportion 133-2 of the third photoresist 133, the third hole injectionlayer 143, the third hole transport layer 153, the third emission layer163, and the third buffer layer 173, which are formed in the secondportion 133-2 of the third photoresist 133, are removed, and the thirdhole injection layer 143, the third hole transport layer 153, the thirdemission layer 163, and the third buffer layer 173, which are formed onthe third pixel electrode 103, remain as a pattern.

Since the third lift-off layer 123 includes a fluoropolymer, a thirdsolvent including fluorine is used in the lift-off process.Additionally, since the lift-off process is performed after theformation of the third emission layer 163, a material having lowreactivity with the third emission layer 163 may be used as the thirdsolvent. Additionally, the third solvent may include a hydrofluoroether,like the first solvent.

However, in spite of using a material having low reactivity with thethird emission layer 163 as the third solvent, there is a problem inthat the third emission layer 163 may be damaged during the lift-offprocess due to a component that decomposes (or dissolves) an organicmaterial.

Concurrently, there is a problem in that damage to the first emissionlayer 161 and the second emission layer 162 may be accumulated becausethe first emission layer 161 and the second emission layer 162 that arefirst formed in the previous structures are exposed to the third solventin the lift-off process included in the third unit process, and exposedto the lift-off process several times as each unit process is repeatedfor each pixel.

Accordingly, in the organic light-emitting display apparatus accordingto an embodiment and a manufacturing method thereof, since the firstbuffer layer 171 is formed on the first emission layer 161, the secondbuffer layer 172 is formed on the second emission layer 162, the thirdbuffer layer 173 is formed on the third emission layer 163, and thefirst buffer layer 171, the second buffer layer 172, and the thirdbuffer layer 173 serve as barriers, damage to the respective emissionlayers during the lift-off process may be reduced.

Referring to FIG. 10E, end portions of the first hole injection layer141, the first hole transport layer 151, the first emission layer 161,and the first buffer layer 171, which are on the first pixel electrode101, may be aligned with one another. The end portions being alignedwith one another may be understood to be the result of theabove-described manufacturing method. In FIGS. 8D-8G, the first holeinjection layer 141, the first hole transport layer 151, the firstemission layer 161, and the first buffer layer 171 are all patterned byusing the first lift-off layer 121 and the first photoresist 131 as amask through the same opening of the first opening OP1 and the secondopening OP2. Accordingly, all of the first hole injection layer 141, thefirst hole transport layer 151, the first emission layer 161, and thefirst buffer layer 171 may have the same shape (e.g., substantially thesame shape). The same is applied to the second hole injection layer 142,the second hole transport layer 152, the second emission layer 162, andthe second buffer layer 172, which correspond to the second pixelelectrode 102, and the third hole injection layer 143, the third holetransport layer 153, the third emission layer 163, and the third bufferlayer 173, which correspond to the third pixel electrode 103.

Referring to FIG. 11, an electronic control layer 180, an oppositeelectrode 190, a capping layer 200, and an encapsulation layer 210 maybe sequentially deposited, as common layers, on the structure of FIG.10E.

As described above, according to the above-described embodiments, sincedamage to the organic light-emitting device in the manufacturing processis reduced, an organic light-emitting display apparatus having improvedprocess stability and reliability, and a manufacturing method thereof,may be implemented. The scope of the present disclosure is not limitedby the above-described effect.

Spatially relative terms, such as “beneath,” “below,” “lower,” “under,”“above,” “upper,” and the like, may be used herein for ease ofexplanation to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or in operation, in additionto the orientation depicted in the figures. For example, if the devicein the figures is turned over, elements described as “below” or“beneath” or “under” other elements or features would then be oriented“above” the other elements or features. Thus, the example terms “below”and “under” can encompass both an orientation of above and below. Thedevice may be otherwise oriented (e.g., rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein shouldbe interpreted accordingly.

As used herein, the terms “substantially,” “about,” and similar termsare used as terms of approximation and not as terms of degree, and areintended to account for the inherent deviations in measured orcalculated values that would be recognized by those of ordinary skill inthe art. Further, the use of “may” when describing embodiments of thepresent disclosure refers to “one or more embodiments of the presentdisclosure.” As used herein, the terms “use,” “using,” and “used” may beconsidered synonymous with the terms “utilize,” “utilizing,” and“utilized,” respectively. Also, the term “exemplary” is intended torefer to an example or illustration.

Also, any numerical range recited herein is intended to include allsubranges of the same numerical precision subsumed within the recitedrange. For example, a range of “1.0 to 10.0” is intended to include allsubranges between (and including) the recited minimum value of 1.0 andthe recited maximum value of 10.0, that is, having a minimum value equalto or greater than 1.0 and a maximum value equal to or less than 10.0,such as, for example, 2.4 to 7.6. Any maximum numerical limitationrecited herein is intended to include all lower numerical limitationssubsumed therein, and any minimum numerical limitation recited in thisspecification is intended to include all higher numerical limitationssubsumed therein. Accordingly, Applicant reserves the right to amendthis specification, including the claims, to expressly recite anysub-range subsumed within the ranges expressly recited herein.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While one or more embodiments have been described with reference to thefigures, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the present disclosure as definedby the following claims, and equivalents thereof.

What is claimed is:
 1. A display apparatus comprising: a substrate; aplurality of pixel electrodes patterned on the substrate and spacedapart from each other; a pixel defining film defining a pixel area byexposing a center portion of each of the plurality of pixel electrodesand covering an edge of each of the plurality of pixel electrodes; aplurality of hole control layers respectively arranged on the pluralityof pixel electrodes that are exposed through the pixel area; a pluralityof emission layers respectively arranged on the plurality of holecontrol layers; a plurality of buffer layers respectively arrangeddirectly on the plurality of emission layers to physically contact theplurality of emission layers, respectively, each of the plurality ofbuffer layers having a highest occupied molecular orbital (HOMO) energylevel greater than the HOMO energy level of each of the plurality ofemission layers; and an opposite electrode integrally provided over theplurality of buffer layers, wherein end portions of the plurality ofhole control layers, the plurality of emission layers, and the pluralityof buffer layers, which are on any one of the plurality of pixelelectrodes, are aligned with one another.
 2. The display apparatus ofclaim 1, wherein a lowest unoccupied molecular orbital (LUMO) energylevel of each of the plurality of buffer layers has a value between awork function of the opposite electrode and the LUMO energy level ofeach of the plurality of emission layers.
 3. The display apparatus ofclaim 1, wherein each of the plurality of hole control layers comprisesat least one selected from a hole injection layer (HIL) and a holetransport layer (HTL).
 4. The display apparatus of claim 1, furthercomprising an electronic control layer that is integrally providedbetween the plurality of buffer layers and the opposite electrode. 5.The display apparatus of claim 4, wherein the lowest unoccupiedmolecular orbital (LUMO) energy level of each of the plurality of bufferlayers has a value between the LUMO energy level of the electroniccontrol layer and the LUMO energy level of each of the plurality ofemission layers.
 6. The display apparatus of claim 4, wherein theelectronic control layer comprises at least one selected from anelectron injection layer (EIL) and an electron transport layer (EML). 7.The display apparatus of claim 1, wherein the plurality of buffer layerscomprise a low molecular weight organic material.
 8. The displayapparatus of claim 1, wherein the plurality of buffer layers comprise anelectron transport material.
 9. The display apparatus of claim 1,wherein the plurality of buffer layers comprise a metal oxide material.10. The display apparatus of claim 1, wherein the plurality of pixelelectrodes comprise a first pixel electrode configured to emit redlight, a second pixel electrode configured to emit green light, and athird pixel electrode configured to emit blue light, and the pluralityof emission layers comprise a red emission layer provided correspondingto the first pixel electrode, a green emission layer providedcorresponding to the second pixel electrode, and a blue emission layerprovided corresponding to the third pixel electrode.